PROJECT SUMMARY Breast cancer is the most common cancer among women in the world. When breast cancer is found in early stages, it can be effectively treated or even cured, but treating a patient in later stages is very difficult. Thus, early detection of breast cancer is critical. Mammography is the current gold standard for breast cancer screening; however, most women with abnormal mammograms are eventually found not to have breast cancer. Fewer than 5 per 1,000 women actually have the disease when they are screened. Therefore, most abnormal mammograms are false positives that require further investigations including expensive breast imaging and biopsies, which can cause psychological distress. According to the American Cancer Society (ACS), about 10% of women who have a mammogram will be called back for more tests, but only 8% to 10% of those women will need a biopsy and 80% of those biopsies turn out to be benign. Therefore, the vast majority of the women would have undergone unnecessary investigations. Our aim is to identify circulating lipid and miRNA signatures that can be used reliably as a companion diagnostic tool together with screening mammography to reduce the number of unnecessary follow-up investigations, especially invasive biopsy. In our preliminary studies, we have identified a panel of 15 plasma lipid species that were able to distinguish early stage of cancer from benign lesions with over 90% accuracy. Using a ratio based normalization method, we have also found 5 paired plasma miRNA ratios that differentiate breast cancer from benign samples with over 90% accuracy. In order to validate our existing markers and identify potential novel markers, as well as integrate lipid and miRNA markers to increase the accuracy for early detection of breast cancer, we propose the following aims: 1. Validate and test the predictive value of circulating lipid markers for early detection of breast cancer. 2. Establish circulating miRNA markers for early detection of breast cancer. 3. Integrate circulating lipid and miRNA markers for early detection of breast cancer.